Preoperative anemia as a marker of postoperative outcomes: a retrospective cohort study

Immich, Liege Caroline; Law, Liliane Ghi Mei; Ouriques, Igor Heineck; Pimentel, Yan Prates; Menegon, Christian Camatti; Mendes, Florentino Fernandes

doi:10.1016/j.bjane.2026.844747

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Original Investigation • Braz. J. Anesthesiol. 76 (2) • 2026 • https://doi.org/10.1016/j.bjane.2026.844747 linkcopy

Preoperative anemia as a marker of postoperative outcomes: a retrospective cohort study

Authorship SCIMAGO INSTITUTIONS RANKINGS

Background Preoperative anemia is common and associated with adverse postoperative outcomes.

Objective To evaluate the association between preoperative anemia severity and clinical outcomes in patients undergoing elective noncardiac surgery.

Methods This retrospective cohort included 23,579 adults assessed preoperatively between January 2015 and August 2025, all with documented hemoglobin (Hb) and hospitalized for noncardiac surgery. Patients were stratified as no anemia (≥ 13 g.dL⁻¹), mild (11.1‒12.9 g.dL⁻¹), moderate (8.1‒11.0 g.dL⁻¹), or severe anemia (≤ 8.0 g.dL⁻¹). Outcomes were in-hospital mortality, Intensive Care Unit (ICU) admission, and Length of Stay (LOS). Analyses used Poisson regression with robust variance adjusted for confounders.

Results Among the participants, 15,909 (67.5%) had no anemia, 6,396 (27.1%) mild, 1,174 (5.0%) moderate, and 100 (0.4%) severe anemia. Overall, 62.6% were female, and the mean age was 60.7 years (SD ±15.4). Compared with no anemia, all anemia categories were independently associated with higher in-hospital mortality, increased ICU admission, and longer LOS. Severe anemia was the strongest predictor of in-hospital mortality (adjusted RR = 24.7; 95% CI 13.3‒46.0; p < 0.001). Intermediate or major surgeries (RR = 4.7; 95% CI 3.4‒6.6), age > 54 years (RR = 4.4; 95% CI 2.6‒7.6), and male sex (RR = 2.1; 95% CI 1.6‒2.9) were also independent predictors of in-hospital mortality.

Conclusions Preoperative anemia, even when mild, was independently associated with higher in-hospital mortality, greater ICU admission, and prolonged hospitalization. These results support systematic screening and targeted management, including Patient Blood Management (PBM) strategies, to improve perioperative outcomes.

KEYWORDS
Anemia; Anesthesiology; Elective surgical procedures; Preoperative care; Postoperative complications

Total sample	Overall cohort (n = 23,579)	No anemia (n = 15,909)	Mild (n = 6,396)	Moderate (n = 1,174)	Severe (n = 100)	p-value
Age (years)	60.7 ± 15.4a	60.2 ± 15.1a	61.2 ± 15.8a	64.0 ±1 6.0b	58.8 ± 18.2a	< 0.001*
Sex						< 0.001**
Female	14,768 (62,6%)a	8,619 (54.2%)a	5,270 (82.4%)b	814 (69.3%)^c	65 (65.0%)a,c
Male	8,811 (37.4%)a	7,290 (45.8%)a	1,126 (17.6%)b	360 (30.7%)^c	35 (35.0%)a,c
ASA-PS						< 0.001**
I ‒ II	20,353 (87.8%)	14,200 (90.7)a	5,370 (85.3%)b	740 (64,5%)^c	43 (44.8%)^d
III ‒ V	2,840 (12.2%)a	1,453 (9.3%)a	926 (14.7%)b	408 (35.5%)^c	53 (55.2%)^d
Procedure complexity						< 0.001**
Minor	15,515 (65.8%)a	10,582 (66.5%)a	4,179 (65.3%)a	699 (59.5%)b	55 (55.0%)a,b
Intermediate	7,647 (32.4%)a	5,065 (31.8%)a	2,106 (32.9%)a	435 (37.1%)b	41 (41.0%)a,b
Major	417 (1.8%)a	262 (1.6%)a	111 (1.7%)a	40 (3.4%)b	4 (4.0%)a,b
Comorbidities
Hypertension	10,502 (46.4%)a	6,699 (43.8%)a	3,038 (49.7%)b	705 (62.6%)^c	60 (64.5%)^c	< 0.001**
DM	3,507 (14.9%)a	2,134 (13.4%)a	1,072 (16.8%)b	273 (23.3%)^c	28 (28.0%)^c	< 0.001**
PMI	880 (3.7%)a	558 (3.5%)a	247 (3.9%)a	67 (5.7%)b	8 (8.0%)a,b	< 0.001**
Hypothyroidism	1,746 (7.4%)a	1,052 (6.6%)a	581 (9.1%)b	105 (8.9%)b	8 (8.0%)a,b	< 0.001**
Hyperthyroidism	100 (0.4%)	64 (0.4%)	32 (0.5%)	4 (0.3%)	‒	< 0.642
CKD	945 (4.5%)	305 (2.1%)a	345 (6.1%)b	261 (25.3%)^c	34 (38.6%)^d	< 0.001**
Hb-S (days)	26.7 (7.9‒90.9)	27 (8‒92)	24 (8‒87)	28 (10‒89)	31 (11‒77)	< 0.086***

Overall sample	No anemia (n = 15,909)	Anemia (n = 7,670)	p-value
In-hospital mortality, n (%)	78 (0.5%)	102 (1.3%)	< 0.001a
ICU admission, n (%)	514 (3.2%)	453 (5.9%)	< 0.001a
LOS, median (IQR)	1.0 (0.3 - 2.1)	1.0 (0.3 - 2.3)	< 0.001b

Intermediate or major surgeries	No anemia (n = 5,327)	Anemia (n = 2,737)	p-value
In-hospital mortality, n (%)	65 (1.2%)	69 (2.5%)	< 0.001a
ICU admission, n (%)	452 (8.5%)	368 (13.4%)	< 0.001a
LOS, median (IQR)	2.1 (1.0 - 4.1)	2.2 (1.0 - 5.2)	< 0.001b

Total sample	No anemia (n = 15,909)	Mild (n = 6,396)	Moderate (n = 1,174)	Severe (n = 100)	p-value
In-hospital mortality, n (%)	78 (0.5%)a	64 (1.0%)b	27 (2.3%)^c	11 (11.0%)^d	< 0.001*
ICU admission, n (%)	514 (3.2%)a	304 (4.8%)b	128 (10.9%)^c	21 (21.0%)^d	< 0.001*
LOS, median (IQR)	1.0 (0.3 - 2.1)a	1.0 (0.3 - 2.2)b	1.2 (0.4 - 5.0)^c	1.3 (0.3 - 8.0)^c	< 0.001**

Intermediate or major surgeries	No anemia (n = 5,327)	Mild (n = 2,217)	Moderate (n = 475)	Severe (n = 45)	p-value
In-hospital mortality, n (%)	65 (1.2%)a	42 (1.9%)a	22 (4.6%)b	05 (11.1%)b	< 0.001*
ICU admission, n (%)	452 (8.5%)a	245 (11.1%)b	110 (23.2%)^c	13 (28.9%)^c	< 0.001*
LOS, median (IQR)	2.1 (1.0 - 4.1)a	2.1 (1.0 - 4.4)b	3.9 (1.2 - 9.0)^c	5.1 (0.6 - 14.4)a,b,c	< 0.001**

	Overall sample		Intermediate or major surgery subgroup
Factors	RR (95% CI)	p-value	RR (95% CI)	p-value
Anemia
Severe	24.7 (13.3 - 46.0)	< 0.001	10.9 (4.4 - 27.4)	< 0.001
Moderate	4.6 (3.0 - 7.1)	< 0.001	3.6 (2.2 - 5.9)	< 0.001
Mild	2.5 (1.8 - 3.5)	< 0.001	1.7 (1.1 - 2.5)	< 0.011
No anemia	1		1
Sex
Male	2.1 (1.6 - 2.9)	< 0.001	1.5 (1.0 - 2.1)	< 0.036
Female	1		1
Procedure complexity
Major	4.7 (3.4 - 6.6)a	< 0.001a	4.8 (3.2 - 7.1)	< 0.001
Intermediate	4.7 (3.4 - 6.6)a	< 0.001a	1
Minor	1		-	-
Age
> 54 years	4.4 (2.6 - 7.6)	< 0.001	3.8 (2.0 - 7.1)	< 0.001
≤ 54 years	1		1

	Overall sample		Intermediate or major surgery subgroup
Factors	RR (95% CI)	p-value	RR (95% CI)	p-value
Anemia
Severe	4.2 (2.9 - 6.3)	< 0.001	3.0 (1.8 - 4.9)	< 0.001
Moderate	2.4 (2.0 - 2.9)	< 0.001	2.3 (1.8 - 2.8)	< 0.001
Mild	1.5 (1.3 - 1.8)	< 0.001	1.4 (1.2 - 1.6)	< 0.001
No anemia	1		1
ASA-PS
III ‒ V	2.7 (2.4 - 3.1)	< 0.001	2.0 (1.7 - 2.3)	< 0.001
I ‒ II	1		1
Sex
Male	1.8 (1.6 - 2.1)	< 0.001	1.7 (1.5 - 1.9)	< 0.001
Female	1		1
Procedure complexity
Major	9.0 (7.6 - 10.8)a	˂0.001a	3.8 (3.2 - 4.4)	< 0.001
Intermediate	9.0 (7.6 - 10.8)a	˂0.001a	1
Minor	1		-	-
Age
> 54 years	1.7 (1.5 - 2.1)	< 0.001	1.7 (1.4 - 2.1)	< 0.001
≤ 54 years	1		1

	Overall population		Intermediate or major surgery subgroup
Factors	RR (95% CI)	p-value	RR (95% CI)	p-value
Anemia
Severe	3.0 (2.3 - 3.8)	< 0.001	2.1 (1.6 - 2.8)	< 0.001
Moderate	2.3 (2.1 - 2.5)	< 0.001	1.9 (1.7 - 2.1)	< 0.001
Mild	1.4 (1.3 - 1.6)	< 0.001	1.3 (1.2 - 1.4)	< 0.001
No anemia	1		1
METs
Moderate-to-high	0.6 (0.6 - 0.7)	< 0.001	0.8 (0.7 - 0.8)	< 0.001
Low	1		1
Sex
Male	1.8 (1.7 - 1.9)	< 0.001	1.7 (1.5 - 1.8)	< 0.001
Female	1		1
Procedure
Major	4.5 (4.2 - 4.9)a	< 0.001a	1.6 (1.4 - 1.8)	< 0.001
Intermediate	4.5 (4.2 - 4.9)a	< 0.001a	1
Minor	1		-	-
Age
> 54 years	1.7 (1.5 - 1.9)	< 0.001	1.9 (1.7 - 2.1)	< 0.001
≤ 54 years	1		1

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[1] *Independent t-test; **Chi-Square; ***Kruskal-Wallis test.

[TFN1] ^a,b
Different letters indicate statistically significant differences.

DM, Diabetes Mellitus; PMI, Previous Myocardial Infarction; CKD, Chronic Kidney Disease; Hb-S, Hemoglobin-to-surgery interval: median and Interquartile Range (IQR).